I am sorry for the loss of both your father and cousin. The bottom line is that likely have recourse.
The end result will be that your father's estate will need to litigate against your cousin's estate. The easier way to proceed would be to get your cousin's wife to just pay the assets over to the executor of your father's estate. However, her lawyer will likely tell her that she should not do that, and therein lies why the litigation will be necessary.
The first thing that you need to do is touch base with an attorney to get appointed to administer your father's estate. Once appointed, you need to get control of your father's former bank account statements. Then you will be looking at the appropriateness of the transactions. Once you can prove that the funds were misappropriated, the rest of the work begins on recovery of those funds.
Please let me know if I can help.
The one thing I need to add to Attorney Snell's answer is that you MUST watch out for the special statute of limitations that generally applies to lawsuits brought against someone who has died for the wrongful acts committed during lifetime. Generally, you MUST file the lawsuit and serve notice within one year from date of death. I would need to research to determine if there is any exception for the wrongs committed by a dead attorney-in-fact. You need to speak with an attorney who regularly handles probate litigation cases. Good luck.
E. Alexandra "Sasha" Golden is a Massachusetts lawyer. All answers are based on Massachusetts law. All answers are for educational purposes and no attorney-client relationship is formed by providing an answer to a question.
Echoing the answers of the prior two attorneys, your cousin was acting as a fiduciary under the power of attorney - unless that power of attorney authorized him to make gifts to himself, he would have no authority to transfer assets to himself, without your father's express permission. He would liable for his breaches of his fiduciary responsibilities. As noted, there are time limitations, both statutory and practically. You should gather together your records and facts and contact a probate attorney promptly. Good luck.